Resistive termination



Jam 17 1950 s. ROSEN 3 3 I RESISTIVE TERMINATION Filed March 10, 1945 FIG.

m/vmvrop 5. ROSE N ATTOPNE 3 Patented Jan. 17, 1950 RESISTIVE TERMINATION Sidney Rosen, Rockville Centre, N. Y., .assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application March 10, 1945, Serial No. 582,113

3 Claims. (01. 178-44) This invention relates to coaxial transmission lines and more particularly to a resistive termination for such lines. H

' The object of the invention is to reduce the reactance inherently associated with a resistive termination for a coaxialtransmission line.

There is often required for a coaxial transmission line a resistive termination which will have the least possible amount of associated reactance. However, the resistive material forming thetermination must, in general, be associated with a mechanical supporting member. The presence of the supporting member, due to its dielectric properties, introduces an undesired capacitance effectively in shunt with the resistance.

In accordance with the present inventionthis unwanted capacitance is reduced to a minimum by making the supporting member in the form of a strip of insulating material which is diametrically connected between the outer conductor and the inner conductor of the line. The resistance is provided by coating the strip with resistive material. Means are provided for clamping the ter mination at its center to the inner conductor and at its ends to the outer conductor. To insure good electrical connections at these points the termination may be metalized at the center and at the ends.

The nature of the invention will be more fully understood from the following detailed description and by reference to the accompanying drawings, in which like reference characters refer to similar or corresponding parts and in which:

Fig. 1 shows a longitudinal cross-section of an attenuator comprising sections of coaxial transmission line with resistive terminations in accordance with the invention; and

Fig. 2 is a view of the termination alone.

The attenuator of Fig. 1 comprises a tube I in which are two sections of coaxial transmission line 2. Each section 2 is made up of a tubular outer conductor 3 and a concentric inner conductor 4, held in position at the outer end by the insulating spacer 6. At the inner end each section 2 is terminated by a resistor l which is connected diametrically between the ends of the conductors 3 and 4. The resistor 1 is clamped in place at its center by means of a stud 8 having a threaded end 9 of smaller diameter which passes through a hole in the resistor l and screws into a tapped hole I I in the end of the central conductor 4. The ends of the resistor l are clamped against the end of the outer conductor 3 by means of the collar 12 which screws onto the reduced end of the conductor 3 and has an inwardly extending radial z flange l3 which grips the ends of the resistor 1. Mounted on the end of each stud 8 is a metal disc 14.

As shown more clearly inthe larger scale view of Fig. 2, the resistor 1 consists of a stri of insulating material l6 coated with resistive material H. The insulating material [6 should have high mechanical strength so that its cross-section may be made small, and a low dielectric constant, to minimize the capacitance introduced. A satisfactory material for this purpose is a suitable glass or an infusible organic synthetic resin such as a cured phenolformaldehyde condensation product, for example, Bakelite. The resistive material Il may, for example, be carbon or Nichrome. Contact surfaces l8 are provided at the ends and the center by applying a coat of silver or other metal paste over the resistive material H. The resistance of the resistor I may be adjusted to the required value by gradually removing the material l'l, as for example, by scraping. A central hole I!) is provided for the threaded end 9 of the stud 8 to pass through, as explained above.

In order to avoid setting u an undesired transverse electric field in the space between the two line sections 2, the resistor 1 should have both physical and electrical symmetry about the transverse center line 20. Under these circumstances the transverse electric field produced by current flowing between the outer conductor 3 and the inner conductor 4 through one-half of the resistor I is cancelled by that produced by the current through the other half.

By making the resistor I in the form of a strip,

- a minimum amount of supporting insulating maof alternating electromotive force E is connected to the outer end of one of the coaxial sections 2, say between a point 2| on the outer conductor 3 and a point 22 on the inner conductor 4. A load R is similarly connected to the outer end of the other coaxial section 2, as at the points 23 and 24. The diameter of the tube l is so small that waves of the frequency of the source E will not be transmitted directly through the section of wave guide 24 between the two coaxial sections 2. However, the left-hand disc l4 will act as a radiator to establish the desired transverse magnetic field in the space between the two discs l4, and the right-hand disc l4 serves as a target for picking up the energy. The attenuation introduced depends upon the distance between the two discs l4 and is approximately proportional to this distance. The attenuation may be varied, as desired, by sliding one or both of thelinesections 2 within the tube 1.

What is claimed is:

1. In combination, means for establishing a magnetic field, an energy pick-up device ,ppsitioned Within said field, a coaxial transmission line, and a substantially purelyiresistive terminae tion, said line comprising a tubular ,outer, con,- ductor and an inner conductor concentric there- 'ing a low dielectric constant to minimize the cawith, said pick-up device being.,-connectedto an end of said inner conductor, said termination comprising a strip of insulating material coated with resistive material, saidstrip being connected diametrically between said outenconductor and said inner conductorin proximity to said pickupdevice, said insulating material being of minimum cross-section consistent. with mechanical strength and having a low dielectric constant to minimize the capacitance introduced, thereby, and said termination havingiphysical and .elec-, trical symmetry about its transverse center line to minimize the inductive, .efiects associated therewith, wherebywavereflection and the frequency-dependence of. the phaseuangleof said termination are minimized.

2. An attenuator comprising. a conducting tube, means for establishing a transverse magnetic field therein, an inner conductor concentrio with said tube, an electrodeeonnectedtoan pacitanceintroduced thereby, and said termination having physical and electrical symmetry about its transverse center line to minimize the ;inductive effects associated therewith.

3. An attenuator in accordance with claim 2 in which the position of said electrode within said tube is adjustable longitudinally to vary the attenuation.

SIDNEY ROSEN.

REFERENCES CITED The following references are of record in the file: of this patent:

UNITED STATES PATENTS Number Name: Date 1,954,355 Handy Apr. 10,1934 1,957,538 Jensen May 8,1934- 2,41 9,537 Christensen Apr. 29,1947 2,434,560 Gunter Jan. 13, 1948 2,451,201 Clark ,Oct. 12,, 1948 FOREIGN PATENTS Number Country Date 295,444 Great Britain Aug. 13, 1928 

